Typically, when an end user specifies a compression need from a manufacturer the manufacturer tries to provide a unit from an available product line to meet the performance and price parameters given. Since the potential applications and the specific parameters given by different users can vary, each unit may be specifically built for a unique application. For example, in a drive system, the final driven speed for a unit can vary. Generally, various components of the drive system to be installed in a gearbox have to be individually assembled and aligned with significant precision to prevent premature wear and failure. The assembly in the gearbox includes inner bearings and outer housings, a driven pinion/shaft, oil seals, an impeller to go into the gearbox housing with a gas seal around the shaft, associated bits and pieces of the oil lubrication system, and a shaft end cap and associated fittings.
Assembling these components for every unit is labor intensive and therefore expensive. It requires stocking of many options for given components that can be assembled together in only so many discrete ways. This requires greater costs for storage, proper inventory and, most of all, in assembly costs for a given unit.
Another costly issue is the need to precision fabricate all the components to facilitate the alignment procedure. The individual part tolerances can add up, making the ultimate alignment more difficult. A failure to properly control alignment can result in premature bearing, seal, or gear set wear. Manually assembling and aligning each unit can be a significant portion of the total labor cost.